One of the best episodes of the series. Kind of a mix between the Star Trek episodes "The Enemy Within" and the "Alternative Factor". Guy Williams and Mark Goddard finally have something to do in this episode besides being exasperated at Smith.
You've got to wonder what the series would have been like had the series not been taken over by the Will, Dr. Smith, Robot "troika".
BTW, when Will and the Robot first visit the anti-matter world and are "attacked" by the moving rocks, if you look closely you can CLEARLY see the shadow of one of the stage hands pushing one of the rocks.